passive v. active preamps, could use some input

maxwalrath · « **on:** 22 Mar 2004, 06:42 pm »

Here's my system...

Technics DVD-A10, heavily modded by modwright
Modwright Beta pre
Odyssey Stratos w/cap upgrade
VMPS RM1
All Bolder cables and power cords

I'm in a little bind for cash, and thinking about my system, I realize I could be happy having only one set of inputs. 95% of my listening is done through the Technics, I would just switch cables to my TV for The Soprano's and Eagles games. I've been looking into the Luminous Audio AXIOM passive pre. It looks to be as simple as things come, no power cord, just one set of ins and outs and a volume control. One other advantage for me is that I only have two Bolder power cords, going with a passive would free up one of them to replace the stock cord on the Stratos.

I've never had a passive, what are the advantages and drawbacks? Are there any worthwhile competitors to the AXIOM, keeping in mind it costs about $150 with the caddock resistor upgrade?

Here's a link to the audiogon ad for the AXIOM... http://cls.audiogon.com/cgi-bin/cls.pl?preatran&1084720009

Thanks!
Max

rkapadia@ROOP · « **Reply #1 on:** 22 Mar 2004, 08:22 pm »

Max,

The general stereotypes for passive are preservation of tonal accuracy at the expense of life-like dynamics. Also, passive preamplifiers are much more sensitive to impedance mismatch.

Active preamplifiers may suffer from absolute tonal accuracy but maintain dynamics better than passive counterparts. Active preamplifiers are generally required when the input has a high "input impedance"

I haven't found the above to be true necessarily, but those are generally the points you'll see depending on 1) what sound qualities somebody prefers and 2) if the person posting owns a passive or active (because each and every one of us owns the best possible

).

Good luck with your decision; I'm surprised the modWright beta isn't to your satisfaction.

Regards,

ooheadsoo · « **Reply #2 on:** 22 Mar 2004, 08:27 pm »

Quote from another forum: The general ideal condition for a passive pre is a short cable run, a high (4V-ish) output from your source, and an easy amplifier input impedence.

Everything I've heard about the Axiom has been positive. In a passive system though, system matching is extremely important. I read an article saying that the output impedance of the source should be really low. Symptoms of the output impedance not being low are supposed to be smeared transients, highs that are damped. With my Adcom SLC-505 passive preamp and my Sony SCD-CE775, I had that exact scenario. The highs were just plain missing and the soundstage was smeared. Now supposedly the Sony is a pretty good candidate for passive preamps, so the other issue is long cable runs. I have a 1 meter run from the cdp to the preamp and a 1.5m run from the preamp to the poweramp, which is probably way too long. The end result is that the passive preamp sounded terrible in my system. I solved my particular problem by bumping up the sensitivity on my power amp, but that might not work for everyone.

Some people complain about reduced dynamics and bass control with a passive pre, but I have not experienced this in my system. Some people also complain about their systems not being loud enough. Again, not the case with my system. It plays pretty much as loud as my old active preamp, meaning I listen around 8 to 10 oclock on the volume dial under normal circumstances. Again, system matching is crucial.

The biggest advantage I got with my passive pre was reduced hiss (basically no hiss from the passive pre,) whereas my old active preamp hissed at me like a cat in the nearfield.

The downside of using the passive pre in my system is that I can hear my power amp hum through my speakers sometimes at the higher sensitivity setting.

I'm planning to go back to an active later, since I don't like hearing the hum, even if it's intermittent.

If your Technics can drive your poweramp without a preamp and your cable runs are short, it may be worth it for you to give it a shot and find out if they have a return policy. YMMV.

maxwalrath · « **Reply #3 on:** 22 Mar 2004, 08:33 pm »

things the axiom passive doesn't have...

1. an on/off switch
2. an iec adaptor
3. ac/dc conversion
4. a source selector
5. about 10 less rca's
6. an led

maxwalrath · « **Reply #4 on:** 22 Mar 2004, 08:35 pm »

Roop, I actually preferred the modwright to the minimax in my system. I just think I can get by with one set of ins and outs, and if I could save some $$ to boot it would be great.

mattybumpkin · « **Reply #5 on:** 22 Mar 2004, 08:47 pm »

I have been kicking around the idea of the Axiom with the Caddock upgrade, only $150 total.

FYI - Tim at Luminous customizes the pre to your gear to minimize/eliminate mismatch.

Regards,

"M"

zybar · « **Reply #6 on:** 22 Mar 2004, 09:55 pm »

In the right system I have found a passive very hard to beat. It doesn't suffer from lack of dynamics as some suggest. In fact, the Placette Passive I currently have is MORE dynamic than the AVA T7 active hybrid preamp or the MiniMax all tube preamp in my system.

The drawback to the passive is that you do have to be careful about proper system matching. Things you normally don't think about like ic/cable capacitance, input impedance, amp sensitivity, etc... all now come into play with a passive.

At the end of the month I should have in the Bent NOH passive. I am hoping that takes my system to an even higher level...

George

ooheadsoo · « **Reply #7 on:** 22 Mar 2004, 10:08 pm »

I had actually inquired about a DIFFERENT passive preamp before (Channel Island Audio VPC-1) and this is what they told me about impedance mismatch:

Passive preamps are basically all the same when it comes to impedance matching. If the Adcom does not work why are you still trying to stay with a passive?

I asked him because Axiom had said something about matching gear and stuff, but I can't deal with the single input that the Axiom has. If you do try the Axiom, be sure to let us know how it goes!

As far as dynamics, I have a hard time listening to classical music at low levels with my passive preamp. If I set the volume so that I can just hear the soft passages, the loud passages are too loud, and people can hear it throughout the house. If I tone it down so that the loud passages are softer, then I can no longer hear the soft passages. It's actually pretty annoying late at night.

zybar · « **Reply #8 on:** 22 Mar 2004, 10:10 pm »

Sounds like a bad implementation.

I do NOT have to crank the volume to get excellent bass with the Placette.

George

ooheadsoo · « **Reply #9 on:** 22 Mar 2004, 10:11 pm »

I don't have any bass issues with my passive either, and it's a cheapo one too.

zybar · « **Reply #10 on:** 22 Mar 2004, 10:14 pm »

Ok, so what does this mean?

Quote

As far as dynamics, I have a hard time listening to classical music at low levels with my passive preamp. If I set the volume so that I can just hear the soft passages, the loud passages are too loud, and people can hear it throughout the house. If I tone it down so that the loud passages are softer, then I can no longer hear the soft passages. It's actually pretty annoying late at night.

Not trying to start something, I am honestly confused by your previous post.

George

Jon L · « **Reply #11 on:** 22 Mar 2004, 10:15 pm »

Quote from: zybar

In the right system I have found a passive very hard to beat. It doesn't suffer from lack of dynamics as some suggest. In fact, the Placette Passive I currently have is MORE dynamic than the AVA T7 active hybrid preamp or the MiniMax all tube preamp in my system.

The drawback to the passive is that you do have to be careful about proper system matching. Things you normally don't think about like ic/cable capacitance, input impedance, amp sensitivity, etc... all now come into play with a passive.
...

Which Bent did you get, copper or silver? I once did a A-B comparison between Bent silver TVC vs. Placette passive. Placette is a wonderful piece and has better bass than Bent while sounding very different in presentation. I wouldn't expect one to blow away the other. Let us know later what you think...

ooheadsoo · « **Reply #12 on:** 22 Mar 2004, 10:17 pm »

I'm saying that the dynamic range is so wide that I can't hear the entire piece at *very low volume* because if I can hear the soft passages, the loud passages will be loud enough to be heard throughout the house when everyone else is sleeping.

Meaning that I don't feel the dyamics are restricted at all

zybar · « **Reply #13 on:** 22 Mar 2004, 10:18 pm »

I went with the Copper.

Even if the sound is equally pleasing, I will go with the Bent because it has many more inputs and outputs.

George

zybar · « **Reply #14 on:** 22 Mar 2004, 10:19 pm »

Gotcha!

That's why I shouldn't be doing this while at work.

George

flintstone · « **Reply #15 on:** 22 Mar 2004, 10:49 pm »

Why not try the Technics into your amp first and have a listen..It has a volume control built in. This would give you an idea of how well you will like a passive pre.

Dave

ooheadsoo · « **Reply #16 on:** 22 Mar 2004, 11:00 pm »

I've heard people recommend this before, and it's a fair idea. Actually, if your cdp has a preamp stage built in, you don't need a preamp at all, do you? Otherwise, for systems like mine (without a built in volume control) I would recommend caution because I thought I was going to blow my system when I tried running it straight through. It was way too loud.

zybar · « **Reply #17 on:** 22 Mar 2004, 11:02 pm »

If you want to test to see if your system has enough gain for a passive preamp, take some music that starts VERY SOFTLY and slowly gets louder.

This will allow you to evaluate your gaim without launching some cones across the room.

George

flintstone · « **Reply #18 on:** 22 Mar 2004, 11:10 pm »

The Technics defalt volume is full out-put, you will need to turn it way down before you try this. Your user manual will explain how to axcess it's volume control from your remote.

Dave

Rocket · « **Reply #19 on:** 22 Mar 2004, 11:26 pm »

Hi,

I have listened to systems without a preamp and they definitely don't sound as good when a preamp is re-installed back into the system.

Imo the sound is harsher and less refined.

Just my opinion.

Regards

Rod

Edit: What i meant to mean is when i have heard a preamp in the loop it sounds better imo.